1. Field of the Invention
The present invention relates to a clean box constructed in such structure that objects to be transferred, necessary for production processes of semiconductors, electron-device-associated products, optical disks, etc., can be transferred in a sealed state with a clean gas containing no contaminants and, particularly, in such structure that the objects to be transferred can be transferred or stored in a sealed state with a non-oxidizing gas such as nitrogen gas, an inert gas, or the like so as to prevent oxidation of the objects to be transferred, and also relates to a clean transfer method and apparatus using the clean box.
2. Related Background Art
In general, the clean boxes of this type are arranged to have a box body having an aperture in one surface and an opening/closing lid for hermetically closing the aperture and include those using a mechanical seal with springs or the like for holding the opening/closing lid or those having the structure for vacuum suction of the opening/closing lid with higher adhesion, as described in Japanese Laid-open Patent Application No. 10-321696 (laid open on Dec. 4, 1998) of the invention invented by the same inventor and assigned to the same assignee as the present invention, than in the case of the mechanical seal using the springs or the like.
In use of such clean boxes, it was the conventional practice to put the objects to be transferred, such as semiconductor wafers or the like, in the clean box under the atmospheric pressure in a state filled with the clean air and prevent dust and various fine particles from attaching onto the objects to be transferred by hermetically closing the inside by the opening/closing lid.
Incidentally, with recent decrease in design rules of semiconductors to 0.25 .mu.m or less, the thickness of film has to be controlled in the angstrom order. Particularly, there occurs a phenomenon that an unintended oxide film is naturally formed on a semiconductor wafer when it is exposed only to the atmosphere in the clean box and it becomes hard to control the film thickness in steps thereafter.
For preventing this, there was a technology in which nitrogen gas is introduced into the hermetically closed space while discharging the gas inside the hermetically closed space to the outside, thereby gradually decreasing the concentration of oxygen, but there was no conventional suggestion about a configuration for replacing the gas inside the clean box with nitrogen while maintaining good hermetic sealing.